1. Field of the Invention
The present invention relates to a switch having a housing which receives a temperature-dependent switching mechanism and comprises an electrically conductive lower part as well as an electrically insulating cover part, closing off the lower part and attached thereto, on whose inner side a first countercontact, to which through contact is made externally, is provided for the switching mechanism, the lower part serving as the second countercontact of the switching mechanism which creates, as a function of its temperature, an electrically conductive connection between the two countercontacts.
2. Related Prior Art
A switch of this kind is known from DE 37 10 672 A1.
In the known switch, the housing has a lower part made of metal and a cover part, closing off the lower part, that is made of insulating material. The switching mechanism, which comprises a spring disk that carries a movable contact element, is arranged in this housing. The spring disk operates against a bimetallic disk that is slipped over a movable contact element. Below the switching temperature the spring disk, which is braced against the base of the lower part, presses the movable contact element against a countercontact that is provided on the inner side of the cover part and extends outward, in the manner of a rivet, through the wall of the cover. The base of the lower part serves as a further countercontact for the switching mechanism.
The cover part is held in lossproof fashion on the lower part by means of a crimped rim thereof. Electrical connection is accomplished on the one hand via the outside of the lower part, and on the other hand via the external head of the rivet which passes through the cover.
Since the spring disk itself is made of electrically conductive material, below the response temperature of the switching mechanism it ensures a low-resistance electrically conductive connection between the countercontact on the cover part and the countercontact on the lower part. If the temperature of the switching mechanism is then increased, the bimetallic disk suddenly snaps over and pushes the movable contact element away from the countercontact on the cover part against the force of the spring disk, so that the electrical connection is broken.
Switches of this kind are commonly used for temperature monitoring of electrical devices, and are also called thermal switches. As long as the temperature of the electrical device does not exceed a predetermined response temperature, the switch, which for this purpose is connected in series with the load being protected, remains closed. If the temperature of the load then increases above the response temperature, the bimetallic disk snaps over and thus interrupts the flow of current to the load.
It is a disadvantage of the known switch that it is relatively complex to produce. This is due principally to the fact that after production of the cover part, the countercontact must then be fastened onto the cover part; at the same time, an electrically conductive connection out through the wall of the cover part must be provided. This is done in the manner of a rivet that transitions, outside the cover, into a head to which conductors, crimp terminals, etc. can be soldered. This assembly of the countercontact to the cover part can only be performed manually, and is thus very cost-intensive.
A conductor can now be soldered onto the crimped rim of the lower part as a second connector; it is also possible to weld a crimp terminal onto the outer base of the lower part. These measures can also, as a rule, only be performed manually, so that they also are very cost-intensive.
A further disadvantage of the known switch is the fact that because of the cover part produced from insulating material it is not very pressure-stable, so that it is not suitable for applications where it must withstand high pressures. This is the case, for example, when the switch is arranged in motor windings.
A pressure-stable switch is known from DE 21 21 802 A1. This switch also contains in its housing a temperature-dependent switching mechanism as described above. The housing of this switch comprises a cover part as well as a lower part, both of which are cup-shaped and made of electrically conductive material. Crimp terminals are shaped integrally onto both the upper part and the lower part, the crimp terminal of the lower part extending outward through a corresponding cutout in the wall of the upper part. An insulating film is arranged between the upper part and lower part in order to insulate the two housing parts electrically from one another.
The temperature-dependent switching mechanism thus makes contact on the one hand with the lower part via the spring disk, and on the other hand with the cover part via the movable contact element, so that an electrically conductive connection exists between the two crimp terminals as long as the temperature of the switching mechanism is below the response temperature. If the temperature of the switching mechanism increases, this electrical connection is broken in the manner described above.
With this switch as well, the need to introduce the insulating film makes final assembly very complex and therefore achievable only manually. This manual final assembly is not only cost-intensive, but also leads to assembly errors and therefore to a high reject rate.
In the case of the switch known from DE 37 10 672 A1, the principal disadvantage is therefore that it is not pressure-resistant, cannot be produced automatically, and moreover is not reliably sealed against dust because of the crimped rim. The switch known from DE 21 21 802 A1 is more pressure-resistant and also better sealed because it is made entirely of metal, but because of the insulation film that is additionally necessary it is even less suited for automatic production.